High efficient single switch single stage power factor correction power supply

ABSTRACT

A single switch PFC power supply (including forward and fly-back power supply) in single stage has two transformers: one forward transformer, one main transformer. The main transformer transfers electrical power from the primary circuit to secondary circuit. The forward transformer is used to correct input current waveform. The two transformer&#39;s primary windings are connected in series. An extra winding of the forward transformer, a capacitor and two diodes are formed a no loss snubber circuit to enhance the efficiency of the power supply.

The present invention relates to a power converter, and more particularly, to a high efficiency power factor correction (PFC) power converter in a single stage.

DESCRIPTION OF THE RELATED ART

Power converters have widely served to convert an unregulated power source to a regulated voltage or current. A PFC (Power Factor Correction) technique is applied to make an input current follow the waveform of an input voltage. Adding a PFC stage to the front end of a power converter substantially avoids unnecessary power loss and heat dissipation in a power contribution system.

Referring to FIG. 1, a power converter having two stages, according to prior art is illustrated. A first stage is PFC stage, which includes an inductor L1, a rectifier D1 and a transistor Q1 is driven by a PFC control signal from the PFC stage. A second stage includes a transistor Q2 controlled by a control signal PWM, a transformer T1 and secondary circuitry, thus output voltage is regulated and output ripple noise is reduced. However, the PFC stage configuration increases the cost and device counts of the converter, and hence the efficiency of power converter is reduced. Therefore, the development trend of a power converter is to build a single stage power converter with PFC function. The present invention provides a single stage PFC converter with no loss snubber circuit that reduces the cost and the size, i.e. device counts, and to improve the converter efficiency. The present invention can further provide a power converter operating in lower stress to obtain higher reliability.

SUMMARY OF THE INVENTION

The first objective of the present invention is to provide a switching power supply that operates from AC line voltage having a power factor correction and output isolation.

The second objective of this invention is to provide for a one stage power factor correction in an AC to DC converter.

The third objective of the present invention is to provide a simple circuit of PFC power supply to reduce the manufacture cost.

The fourth objective of the present invention is to provide a more efficient PFC power supply circuit.

The fifth objective of the present invention is to provide a snubber circuit without loss.

Further objects and advantages of this invention will be apparent from the following detailed description of a presently preferred embodiment, which is illustrated, schematically, in the accompanying drawings.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a schematic of the prior art, the two stage AC to DC converter.

FIG. 2 is an embodiment of the present invention of the primary circuit of single switch power supply.

FIG. 2 a is another arrangement of present invention of the PFC single switch power supply.

FIG. 2 b is yet another arrangement of present invention of the PFC single switch power supply.

FIG. 3 is the present invention of the fly-back or forward power supply of the 120 v AC input.

FIG. 3 a is another arrangement of the present invention of the fly-back or forward power supply of the 120 v AC input.

FIG. 3 b is separated windings arrangement of the present invention of the fly-back or forward power supply of the 120 v AC input.

FIG. 3 c is a circuit arrangement of 120 or 240 of the present invention of the fly-back or forward power supply.

FIG. 4 is an input current waveform of 50 w fly-back power supply.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Before explaining the disclosed embodiment of the present invention in detail, it is to be understood that the invention is not limited in its application to the details of the particular arrangement shown since the invention is capable of other embodiments.

The topology of the present invention is that a (PFC) forward transformer primary winding is connected in series with the main transformer primary winding. The main transformer transfers power from the primary circuit to the secondary circuit, the forward transformer transfers power to its second winding of the forward transformer to correct the input current waveform. When switch is off, the no loss snubber circuit stores the electrical energy in the capacitor; when the switch is on, it relieves the energy to forward transformer.

Refer to FIG. 2: The circuit diagram is a power factor correction for a single switch power supply unit. The arrangement is following:

A full bridge rectifier BD 10 has output terminals(a positive terminal and a negative terminal) and input terminals which are coupled to AC power lines. A first capacitor C10 is coupled to the output terminals of the full bridge rectifier BD20.

An inductor L10 has two terminals, the first terminal and the second terminal which is coupled to the positive output terminal of the full bridge rectifier BD10.

A diode D10 has a cathode and an anode which is coupled to the first terminal of the inductor L10.

A second diode D12 has a cathode and an anode which is coupled to the first terminal of the inductor L10.

A forward transformer T10 has three windings. The second winding T10 p 2 has a first terminal which is coupled to the cathode of the first diode D10 and a second terminal which is coupled to the cathode of the second diode D12. The first winding T10 p 1 has a first terminal and a second terminal which is coupled to the second terminal of the second winding. The third winding T10 p 3 has a first terminal and a second terminal which is coupled to the negative output of the full-bridge rectifier BD10; The second terminals of three windings have the same electrical polarity;

A second capacitor C12 has a positive terminal and a negative terminal, the positive terminal is coupled to the second terminal of the second winding T10 p 2 of the forward transformer T10 and the negative terminal is coupled to the negative output of the full bridge rectifier BD10.

A main transformer T12 has a primary winding and a secondary winding. The first terminal of the primary winding is coupled to the first terminal of the first winding T10 p 1 of the forward transformer T10. The secondary winding of the main transformer T12 is coupled to the secondary circuit. The main transformer can be a forward transformer and fly-back transformer.

A switch Q10 has three terminals, a first terminal, a secondary terminal and a control terminal. The first terminal is coupled to the second terminal of the primary winding of the main transformer T12. The second terminal is coupled to the negative output of the full bridge rectifier BD10. The control terminal is coupled to the PWM or PFM control circuit.

The third capacitor C14 has a first terminal and a secondary terminal. The first terminal is coupled to the first terminal of the switch Q10.

The third diode D14 has an anode coupled the second terminal of the third capacitor C14 and a cathode coupled to the positive terminal of the second capacitor.

The fourth diode D16 has a anode coupled to the terminal of the first winding T10 p 3 of the forward transformer T10, cathode coupled to the second terminal of the third capacitor C14.

The operation of the FIG. 2 is following:

When switch Q10 is on, the third capacitor C14 discharges its electrical energy through the third winding T10 p 3 of the forward transformer T10 and fourth diode D16. A current conducts through the primary winding T10 p 1 of the forward transformer T10 and the primary winding of the main transformer T12 and the switch Q10 and at the same time there is an induced voltage in the second winding T10 s of the forward transformer T10, therefore, there is a current drawn from the input to the second capacitor C12 (charging the second capacitor C12) through the inductor L10, the first diode D10 and the second winding T10 p 2 of the forward transformer T10. When switch Q10 is off, the inductance has a induced voltage and this induced voltage and input voltage force a current charging the second capacitor C12 through the inductor L10 and second diode D12. The leakage inductances of the main transformer T12 primary winding and forward transformer primary T10 p 1 charge the third capacitor C14 through the third diode D14.

The number of the second winding T10 p 2 and the third winding T10 p 3 of the forward transformer T10 is more than two times of the number of the primary winding of the forward transformer T10.

The number of the primary winding T10 p of the forward transformer T10 and value of the inductor L10 is adjusted to certain value to correct the input current waveform in the best shape.

The circuit, comprising of the second winding T10 p 2 of the forward transformer T10, the inductor D10, the second capacitor C12, the first diode D10 and the second diode D12, can have several different arrangements. These arrangements have the same working principle. For example, the circuit arrangement in FIG. 2 a and FIG. 2 b.

The snubber circuit, including the third winding T20 p 3 of the forward transformer T20, the third capacitor C14, the third diode D24 and fourth diode D26, recovers the the energy of leaking inductance of the main transformer T12 and the forward transformer T10, when the switch Q10 is off. It relieves the energy, when the switch Q20 is on. The series connection of the third winding T20 p 3 and the fourth diode can be insert a inductor of small inductance value. The series circuit can have difference arrangement from the FIG. 2. By using this snubber circuit the efficiency of the fly-back power supply can reach as high as 92% for 22v DC output.

The control signal can be a PWM or a PFM signal and the PFM signal has better advantage for designing single stage PFC power supply of a fly-back type power supply.

For 110v AC power the circuit can be arranged as FIG. 3.

The inductor L20 has two terminals and the first terminal is connected to a first power line;

A first diode D20 has an anode and a cathode, the anode is coupled to the second power line.

A third diode D24 has an anode and a cathode, the cathode is coupled to the second power line.

A first transformer T20 has three windings, a first winding T20 p 1, a second winding T20 p 2 and a third winding T20 p 3. The second winding T20 p 2 has a first terminal and a second terminal and a central tap which is coupled to the second power line. A first winding T20 p 1 has a first terminal and a second terminal and a third winding T20 p 3 has a first terminal and a second terminal. The first terminals of the three windings have the same electrical polarity.

A first capacitor C20 has a positive terminal and a negative terminal, the positive terminal is coupled to cathodes of the firs diode D20 and the first terminal of the first winding of the forward transformer, the negative terminal is coupled to the second terminal of the inductor L20.

A second capacitor C22 has a positive terminal and negative terminal, the positive terminal is coupled to the second terminal of the inductor L20 and the negative terminal is coupled to anode of third diode D24.

A second diode D22 has an anode and a cathode, the anode is coupled to the first terminal of the second winding T20 p 2 of the forward transformer T20 and the cathode is coupled to the positive terminal of the first capacitor C20 and the cathode of the first diode D20.

A fourth diode D26 has an anode and a cathode, a cathode is coupled to the second terminal of the second winding T20 p 2 of the forward transformer T20 and the anode is coupled to the negative terminal of the second capacitor C22.

A main transformer T22 has a primary winding and a second winding, the first terminal of the primary winding is coupled to the second terminal of the first winding T20 p 1 of the forward transformer T20. The secondary winding is coupled to secondary circuit. The main transformer can be a forward transformer or a fly-back transformer.

A switch Q20 has a first terminal, a second terminal and a control terminal. The control terminal is coupled to the control circuit which produces PWM or PFM control signal circuit. The first terminal is coupled to the second terminal of the primary winding of the main transformer T22 and the second terminal is coupled to the negative terminal of the second capacitor C22.

A third capacitor C24 has a first terminal and a second terminal. The first terminal is coupled to the first terminal of the switch Q20.

A fifth diode D28 has an anode and a cathode, the anode is coupled to the second terminal of the third capacitor C24 and the cathode is coupled to the positive terminal of the first capacitor C20.

A sixth diode D30 has an anode and a cathode, the anode is coupled to the second terminal of the third winding T20 p 3 of the forward transformer T20 and the cathode is coupled to the second terminal of the third capacitor C24.

The number of the winding of the second winding T20 p 2 and third winding T20 p 3 of the forward transformer T20 is more than two times the number of the winding of the first winding T20 p 1 of the forward transformer.

The operation of the FIG. 3 is following:

When voltage of the second power line is higher than the voltage of the first power line and when the switch Q20 is switched on, the electrical energy in the third capacitor C24 is discharged through the third winding T20 p 3 of the forward transformer T20, the sixth diode D30 and the switch Q20; A current conducts through the primary winding T20 p 1 of the forward transformer T20 and the primary winding of the main transformer T22 and the switch Q20 and at the same time there is an induced voltage in the second winding T20 p 2 of the forward transformer T20, therefore, there is a current drawn from the input to the second capacitor C20 (charging the second capacitor C20) through the inductor L20, the second diode D22 and the second winding T20 p 2 of the forward transformer T20. When switch Q20 is off, the inductor L20 has a induced voltage and this induced voltage and input voltage force a current charging the second capacitor C20 conducts through the inductor L20 and second diode D20. The leakage inductances of the main transformer T22 primary winding and forward transformer primary T20 p 1 charge the third capacitor C24 through the third diode D28.

When voltage of the second power line is lower than the voltage of the first power line and when the switch Q20 is switched on, the electrical energy in the third capacitor C24 is discharged through the third winding T20 p 3 of the forward transformer T20, the sixth diode D30 and the switch Q20. A current conducts through the primary winding T20 p 1 of the forward transformer T20 and the primary winding of the main transformer T22 and the switch Q20 and at the same time there is an induced voltage in the second winding T20 p 2 of the forward transformer T20, therefore, there is a current drawn from the input to the second capacitor C22 (charging the second capacitor C22) through the inductor L20, the fourth diode D26 and the second winding T20 p 2 of the forward transformer T20. When switch Q20 is off, the inductor L20 has a induced voltage and this induced voltage and input voltage force a current charging the second capacitor C22 through the inductor L20 and third diode D24. The leakage inductances of the main transformer T22 primary winding and forward transformer primary T20 p 1 charge the third capacitor C24 through the third diode D28.

The PFC circuit consisted of second winding T20 p 2 of the forward transformer, diodes D20, D22, D24, D25 and the inductor can be have other arrangements for example circuit arrangement of FIG. 3 a.

If the second winding is separated into two equal parts, T20 p 2 and T20 p 3, it can have another arrangement as FIG. 3 b.

If additional component 4 diodes, D30, D31, D32, D33, and a switch S20 are added to above diagram, it can have 120 v or 240 v single switch power supply depended on the switch S20 position as FIG. 3 c. 

What is claimed is:
 1. A single stage PFC fly-back or forward power supply that consists of : A full bridge rectifier with output terminals(a positive terminal and a negative terminal) and input terminals which are coupled to AC power lines; A first capacitor coupled to the output terminals of the full bridge rectifier; An inductor with two terminals, the first terminal and the second terminal which is coupled to the positive output terminal of the full bridge rectifier; A diode with a cathode and an anode which is coupled to the first terminal of the inductor; A second diode with a cathode and an anode which is coupled to the first terminal of the inductor; A forward transformer with three windings, The second winding with a first terminal which is coupled to the cathode of the first diode and a second terminal which is coupled to the cathode of the second diode; The first winding with a first terminal and a second terminal which is coupled to the second terminal of the second winding; The third winding with a first terminal and a second terminal which is coupled to the negative output of the full-bridge rectifier; The second terminals of three windings having the same electrical polarity; A second capacitor with a positive terminal which is coupled to the second terminal of the second winding of the forward transformer and a negative terminal which is coupled to the negative output of the full bridge rectifier; A main transformer with a primary winding and a secondary winding which is coupled to the secondary circuit ; the primary winding with a first terminal which is coupled to the first terminal of the first winding of the forward transformer and a second terminal; The main transformer which is a forward transformer and fly-back transformer; A switch with three terminals, a first terminal which is coupled to the second terminal of the primary winding of the main transformer, a second terminal which is coupled to the negative output of the full bridge rectifier and a control terminal which is coupled to the control circuit; The third capacitor with a first terminal which is coupled to the first terminal of the switch and a second terminal; The third diode with an anode which is coupled the second terminal of the third capacitor and a cathode which is coupled to the positive terminal of the second capacitor; The fourth diode with an anode which is coupled to the first terminal of the third winding of the forward transformer and a cathode which is coupled to the second terminal of the third capacitor.
 2. A single stage PFC fly-back or forward power supply in claim 1, wherein said the primary winding of the forward transformer is coupled in series with the main transformer's primary winding, wherein said energy through primary winding of the forward transformer is used to correct the input current waveform and wherein said energy through the primary winding of the main transformer is transferred to secondary circuit.
 3. A single stage PFC fly-back or forward power supply in claim 2 wherein said the main transformer can be forward transformer or fly-back transformer.
 4. A single stage PFC fly-back or forward power supply in claim 1, wherein said the second winding of the forward transformer is used to draw the current from the input to the storage capacitor, and wherein said the circuit consisting of the second winding of the forward transformer, the first diode, the second diode, the storage capacitor and the inductor have other circuit arrangements.
 5. A single stage PFC fly-back or forward power supply in claim 4, wherein said an inductor is a storage component and wherein said when the switch is on, it stores the electrical energy and wherein said when the switch is off, it relieves the energy through the second diode to the storage capacitor.
 6. A single stage PFC fly-back or forward power supply in claim 1, wherein said the third diode, the fourth diode, third capacitor and third winding of the forward transformer consists of a no loss snubber circuit; and wherein said when the switch is off, it stores energy in the third capacitor and said when the switch is on, it relieves energy from the capacitor to the forward transformer.
 7. A single stage PFC fly-back or forward power supply in claim 6, wherein said fourth diode and the third winding of the forward transformer is used for discharging the third capacitor and there is another arrangement for this discharging circuit that is fourth diode, third winding of the forward transformer and a small value inductor connected in series.
 8. 120v AC A single stage PFC fly-back or forward power supply consist of: An inductor with a first terminal which is connected to a first power line and a second terminal; A first diode with an anode which is coupled to the second power line and a cathode; A third diode with an anode and a cathode which is coupled to the second power line; A first transformer with three windings, A first winding with a first terminal and a second terminal, The second winding consist of a first terminal, a second terminal and a central tap which is coupled to the second power line and a third winding with a first terminal and a second terminal; The first terminals of the three windings have the same electrical polarity; A first capacitor with a positive terminal which is coupled to the cathode of the first diode and to the first terminal of the first winding of the forward transformer and a negative terminal which is coupled to the second terminal of the inductor; A second capacitor with a positive terminal which is coupled to the second terminal of the inductor and a negative terminal which is coupled to the anode of third diode and to the first terminal of the third winding of the forward transformer; A second diode with an anode which is coupled to the first terminal of the second winding of the forward transformer and a cathode which is coupled to the positive terminal of the first capacitor; A fourth diode with an anode which is coupled to the negative terminal of the second capacitor and a cathode which is coupled to the second terminal of the second winding of the forward transformer; A main transformer with a primary winding and a secondary winding, the primary winding with a first terminal which is coupled to the second terminal of the first winding of the forward transformer and a second terminal; The secondary winding which is coupled to secondary circuit; The main transformer is a forward transformer or a fly-back transformer; A switch with a first terminal which is coupled to the second terminal of the primary winding of the main transformer, a second terminal which is coupled to the negative terminal of the second capacitor and a control terminal is coupled to the control circuit which produces PWM or PFM control signal circuit; A third capacitor with a first terminal which is coupled to the first terminal of the switch and a second terminal; A fifth diode with an anode which is coupled to the second terminal of the third capacitor and a cathode with is coupled to the positive terminal of the first capacitor; A sixth diode with an anode which is coupled to the second terminal of the third winding of the forward transformer and a cathode which is coupled to the second terminal of the third capacitor;
 9. 110v AC A single stage PFC fly-back or forward power supply in claim 8, wherein said the primary winding of the forward transformer is connected in series with the primary winding of the main transformer, the energy through the primary winding of the forward transformer is used to correct the input current waveform, the energy through the primary winding of the main transformer is transferred to the secondary circuit.
 10. 120v AC A single stage PFC fly-back or forward power supply in claim 8, wherein said the inductor is used to smooth the input current and when the switch is on, it stores the energy; when the switch is off, it relieves energy to the primary capacitor.
 11. 120v AC A single stage PFC fly-back or forward power supply in claim 8, wherein said the first, the second, the third, the fourth diode, second winding of the forward transformer and the inductor form a rectified and a power factor correction circuit.
 12. 120v AC A single stage PFC fly-back or forward power supply in claim 10, wherein said the first, the second, the third, the fourth diode, second winding of the forward transformer and the inductor have other circuit arrangements.
 13. AC A single stage PFC fly-back or forward power supply in claim 13, wherein said the first, the second, the third, the fourth diode, the inductor and two separating windings of the second winding of the forward transformer have other circuit arrangements.
 14. 120v AC A single stage PFC fly-back or forward power supply in claim 8, wherein said the fifth diode, sixth diode, third capacitor and the third winding of the forward transformer consist of a no-loss snubber circuit; wherein said when the switch is off, it stores energy in the third capacitor and said when switch is on, it relieves energy from the third capacitor to the forward transformer.
 15. 120v AC A single stage PFC fly-back or forward power supply in claim 14, wherein said the third winding of the forward transformer, sixth diode are connected in a series circuit, said when this circuit is inserted with a small value of inductor, it is another arrangement of no loss snubber circuit.
 16. 120v AC A single stage PFC fly-back or forward power supply in claim 13, wherein said four additional diodes and a switch with three terminals is added to the circuit, it is formed a 120v or 240v single switch single stage PFC power supply circuit. 